如何删除变量？ [英] How to delete a variable?
问题描述
这是我的javascript代码，我想删除变量代码，使其值未定义。
var code = $（this）.data（'code'）;
var userelm = $（this）;
这里我正在检查：
< pre class =lang-js prettyprint-override>
if（$（'。code-1'）。val（）！=''&& $（'。code-2'） .val（）！=''&& $（'。code-3'）。val（）！=''）{
if（code == $（'。code-1'）。 val（）+ $（'。code-2'）。val（）+ $（'。code-3'）。val（））{
$（'。overlay'）。remove（）;
$（'。code-box'）。remove（）;
$（'。close-lock'）。remove（）;
userelm.ajaxloader（）; //自己的函数
userelm.off（）;
删除代码;
console.log（代码）;
删除userelm;
}
}
为什么这个程序不会删除代码变量所以它的值是undefined？
在JavaScript中删除变量：
摘要：
您在JavaScript中删除变量时遇到问题的原因是：因为JavaScript不会让你。您不能删除由 var 命令创建的任何内容，除非我们将一只兔子拉出我们的技巧。
delete命令仅适用于未使用var创建的对象属性。
JavaScript允许您在以下条件下删除使用var创建的变量：
-
您正在使用javascript解释器或命令行。
-
您正在使用eval并创建和删除var在那里。
在终端上演示，使用删除boo 或删除（boo）命令。使用 js 命令行终端的演示让你删除变量。
el @ defiant~ $ js
js> typeof boo
undefined
js> boo
typein：2：ReferenceError：boo未定义
js> boo = 5
5
js> typeof boo
number
js>删除（boo）
true
js> typeof boo
undefined
js> boo
typein：7：ReferenceError：boo未定义
如果你必须在JavaScript中将变量设置为undefined，您有一个选项：
javascript页面中的演示：将其放入 myjs.html ：
< html>
< body>
< script type =text / JavaScript>
document.write（aliens：+ aliens +< br>）;
document.write（typeof aliens：+（typeof aliens）+< br>）;
var aliens =争夺尼米兹;
document.write（发现一些外星人：+（外星人类型）+< br>）;
document.write（不是说外星人但是......+外星人+< br>）;
aliens = undefined;
document.write（外星人设置为未定义< br>）;
document.write（typeof aliens：+（typeof aliens）+< br>）;
document.write（你确定他们走了？+外星人）;
< / script>
< / body>
< / html>
使用浏览器打开myjs.html，打印出来：
外星人：undefined
typeof外星人：undefined
找到一些外星人：字符串
不是说外星人但是......争夺nimitz
外星人设置为未定义
typeof外星人：undefined
你确定他们已经离开？ undefined
警告当您将变量设置为时undefined 您正在为另一个变量分配一个变量。如果有人通过运行 undefined ='gotcha！'来中毒，那么无论何时将变量设置为undefined，它都会变为：gotcha！。
我们应该如何检查变量是否没有值？
使用null而不是undefined如下：
document.write（skittles：+ skittles +< br>）;
document.write（typeof skittles：+（typeof skittles）+< br>）;
var skittles = 5;
document.write（skittles：+ skittles +< br>）;
document.write（typeof skittles：+ typeof skittles +< br>）;
skittles = null;
document.write（skittles：+ skittles +< br>）;
document.write（typeof skittles：+ typeof skittles）;
打印：
吃喝玩乐：undefined
类型的吃喝玩乐：undefined
吃喝玩乐：5
类型的吃喝玩乐：数字
吃喝玩乐：null
typeof skittles：object
如果你没有使用strict，你可以删除这样创建的变量：
< script type =text / JavaScript>
//使用严格
a = 5;
document.writeln（typeof a）; //打印号码
删除a;
document.writeln（typeof a）; //打印undefined
< / script>
但如果您取消注释使用严格， javascript将无法运行。
Here is my javascript code, I want to delete the variable code so that it has value undefined.
var code = $(this).data('code');
var userelm = $(this);
Here I'm doing the check:
if($('.code-1').val()!='' && $('.code-2').val()!='' && $('.code-3').val()!=''){
if(code==$('.code-1').val()+$('.code-2').val()+$('.code-3').val()){
$('.overlay').remove();
$('.code-box').remove();
$('.close-lock').remove();
userelm.ajaxloader(); //own function
userelm.off();
delete code;
console.log(code);
delete userelm;
}
}
Why does this program not remove the code variable so it has the value undefined?
Delete a variable in JavaScript:
Summary:
The reason you are having trouble deleting your variable in JavaScript is because JavaScript won't let you. You can't delete anything created by the var command unless we pull a rabbit out our bag of tricks.
The delete command is only for object's properties which were not created with var.
JavaScript will let you delete a variable created with var under the following conditions:
You are using a javascript interpreter or commandline.
You are using eval and you create and delete your var inside there.
Demo on terminal, Use the delete boo or delete(boo) command. A demo with js command line terminal let you delete a variable.
el@defiant ~ $ js
js> typeof boo
"undefined"
js> boo
typein:2: ReferenceError: boo is not defined
js> boo=5
5
js> typeof boo
"number"
js> delete(boo)
true
js> typeof boo
"undefined"
js> boo
typein:7: ReferenceError: boo is not defined
If you MUST set your variable to undefined in JavaScript, you have one option:
Demo in javascript page: put this in myjs.html:
<html>
<body>
<script type="text/JavaScript">
document.write("aliens: " + aliens + "<br>");
document.write("typeof aliens: " + (typeof aliens) + "<br>");
var aliens = "scramble the nimitz";
document.write("found some aliens: " + (typeof aliens) + "<br>");
document.write("not sayings its aliens but... " + aliens + "<br>");
aliens = undefined;
document.write("aliens set to undefined<br>");
document.write("typeof aliens: " + (typeof aliens) + "<br>");
document.write("you sure they are gone? " + aliens);
</script>
</body>
</html>
Open myjs.html with a browser, it prints this:
aliens: undefined
typeof aliens: undefined
found some aliens: string
not sayings its aliens but... scramble the nimitz
aliens set to undefined
typeof aliens: undefined
you sure they are gone? undefined
Warning When you set your variable to undefined you are assigning a variable to another variable. If someone poisons the well by running undefined = 'gotcha!', then whenever you set your variable to undefined, it becomes: "gotcha!".
How should we check if a variable has no value?
Use null instead of undefined like this:
document.write("skittles: " + skittles + "<br>");
document.write("typeof skittles: " + (typeof skittles) + "<br>");
var skittles = 5;
document.write("skittles: " + skittles + "<br>");
document.write("typeof skittles:" + typeof skittles + "<br>");
skittles = null;
document.write("skittles: " + skittles + "<br>");
document.write("typeof skittles: " + typeof skittles);
Which prints:
skittles: undefined
typeof skittles: undefined
skittles: 5
typeof skittles:number
skittles: null
typeof skittles: object
If you are not using strict, you can delete variables created like this:
<script type="text/JavaScript">
//use strict
a = 5;
document.writeln(typeof a); //prints number
delete a;
document.writeln(typeof a); //prints undefined
</script>
but if you uncomment use strict, the javascript will not run.
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